It Began with Babbage Page 12
Zuse recognized that a distinction could be made between a human performing computations and a computing machine. Typical “human habits” could be cast off, and simpler mechanisms, conducive to automatic computation could be used instead. An example was the use of binary arithmetic. Zuse also recognized that scientific and technical computations (in contrast to accounting calculations) may need to deal with numbers ranging from the very small (for example, the coefficient of thermal expansion, e = 0.000012) to the very large (for example, the modulus of elasticity, E = 2,100,000 kg/cm2), with both kinds perhaps appearing in the same computation.68
To accommodate such variation, he proposed the use of “semilogarithmic notation”69—in present-centered language, floating-point representation. Thus, Stibitz was not the original inventor of floating-point notation for numbers (see Section II, this chapter), although it is quite likely that the American did not know of Zuse’s patent application, which meant that he independently (re)invented the concept.
Zuse’s proposal was the basis for his first computer called the Z1, completed in 1938. It was a purely mechanical machine, with a 16-word binary memory, and was the progenitor of his next machine, which combined a mechanical memory with an arithmetic unit made of some 200 electromagnetic relays, and was called the Z2.70 The Z2 was a perforated paper tape-controlled machine that could calculate “certain simple formulae” and demonstrate the “principle of program control,” but it was not a practical computer.71
Zuse’s further work was interrupted temporarily when he was called up for military service. During that time an associate, Helmut Shreyer (1912–1984), an engineer–inventor, began building an electronic version of the Z1 that, using vacuum tubes (“valves” as Shreyer called them), was able to compute at much higher speeds than relays.72
The electronic components in this design were a combination of valves and neon tube diodes. Shreyer built a small binary arithmetic unit with about 100 valves. Unfortunately, the unit was destroyed by war damage.73
A positive outcome of Shreyer’s memorandum was that Zuse was released from military duty and given government backing to pursue his computer research.74 The first fruit of this was the Z3—an electromechanical machine built in Berlin between 1939 and 1941, and financed mainly by the German Aeronautical Research Institute. Unfortunately, it was destroyed in an air raid in 1944.75 Zuse does not tell us the extent to which it was actually in productive operation, save to comment laconically: “A series of interesting programs was tested and calculated on the machine.”76 This machine was controlled by commands punched on paper tapes; its two “parallel” arithmetic units used floating-point binary, 22-bit representation of numbers (a sign bit, a 7-bit exponent, and a 14-bit mantissa).77 The machine not only performed standard arithmetic operations, but also square root extraction and multiplication by common factors such as 2, 1/2, 10, 0.1, and –1. Data were input in decimal form through a keyboard and converted internally to binary, and the reverse was done to produce output results in the form of a “lamp display with four decimal places and a point.”78 A total of 2600 relays were used.
In present-centered language, the Z3 was a single-address machine, with each instruction on the program tape specifying the storage address of a single operand and an operation. Presumably, the second operand was “implied,” an internal register in the arithmetic unit.
The immediate successor to the Z3 was the Z4. Its design, planning, and construction began “immediately” after the completion of the Z3.79 In general architecture, it was “fundamentally” identical to Z3, but with some changes. The word length (in present-centered terminology) was increased to 32 bits; the store was mechanical, and there were “special units for program processing,” although Zuse did not specify what these were. However, he mentioned the addition of conditional branch commands so that, one may presume, these special units included the capacity to execute conditional branches. There were also “various technical improvements.”80 The Z4 was completed in 1945, to the extent that “it could run simple programs.” It was the only one of the wartime Z computers that survived.81 It was also the last of Zuse’s wartime computers. In 1950, after German recovery and reconstruction, the Z4 was transferred to the Eidgenössiche Technische Hochschule (ETH) Zurich,82 but the Z series phylogeny continued on with the Z5, built in the 1950s and still a relay machine, and the later development of electronic successors.83
We will encounter the highly original Zuse later in this chronicle in another context: the development of notation for communicating with the computer—in present-centered language, the development of programming languages.
XII
World War II harbored innumerable secrets. One was the development of an evolutionary series of computers in Bletchley Park, a manor house and estate in what is now the town of Milton Keynes not far from London. Bletchley Park now houses Britain’s National Museum of Computing. During the war, it was the site of that country’s cryptanalytical center, responsible for decrypting codes and ciphers used by the Axis countries. Computing machines played a critical role in Bletchley’s wartime mission. Naturally, the work carried out there was highly classified and remained so long after the war was over.
Like other major technoscientific centers created specifically for the war effort, Bletchley Park was populated by mathematicians, scientists, and engineers, many of whom had either already achieved distinction or would do so in later life. Mathematician Max Newman, whose lectures in Cambridge on Hilbert’s problems had been the catalyst for Turing’s work on computability (see Chapter 4), was one of the team leaders. There was William T. Tutte (1912–2002), who would achieve great distinction for his contribution to combinatorial mathematics. There was Thomas H. Flowers (1905–1998), an electronics engineer who had conducted research on the use of electronic valves (vacuum tubes, in American parlance) in telephone switching networks almost a decade before he entered Bletchley Park.84 There was the eclectic Donald Michie (1923–2007), a classics scholar who, after the war, would turn into a mammalian geneticist before self-transforming into one of Britain’s leading figures in a branch of computer science called artificial intelligence. There was the mathematician and statistician Irving J. Good (1916–200), a student of the renowned Cambridge mathematician Godfrey H. Hardy (1877–1947). There was Allan Coombs (1911–1993), an electronics engineer; and the Welshman Charles Wynn-Williams (1903–1979), a physicist whose doctoral research in the Cavendish Laboratory, Cambridge, was supervised by Lord Ernest Rutherford (1871–1937), and who became especially known before the war for his work on electronic instrumentation for use in nuclear physics and radioactivity research. Among his prewar contributions was the invention of the binary counter, which became a standard component in digital systems, including the digital computer. And there was Alan Turing.
As it turned out, Turing was involved in some of the early computer developments at Bletchley, but not the later work that produced the most significant products.85 Turing’s contributions lay, rather, in actual cryptanalysis—the analysis and deciphering of codes—and with the Enigma—the generic name for a type of electromechanical encryption machine (invented by a German engineer after World War I) and used by such civilian organizations as banks in peacetime, and by both Allied and Axis intelligence during the war. Turing was concerned with deciphering intercepted code produced by the German Enigma.86
The Colossus, a prototype machine, and its production grade, the Mark II Colossus, belong to this story because they were certainly among the very first binary electronic digital computers to be built. They were, in fact, the descendents of a series of earlier machines built at Bletchley Park—the Robinson family, with Heath Robinson as the first, followed by Peter Robinson, and then Robinson & Clearn. The Colossi were followed, as the war came to an end, by other more specialized machines all with quirky names.87
The prototype Colossus, completed in the remarkably short period of about 11 months, became operational in December 1943.88 The Mark II Co
lossus was completed in June 1944, just 5 days before D-Day.89 These machines also interest us because, in Babbage’s country—and Turing’s—they represent England’s first serious engagement with the design and construction of digital computers in the 20th century. As we will see later, they more than compensated for this tardiness by the end of the 1940s.
XIII
At the physical level, as a material artifact, the Colossus had several novel features. It was a binary machine. It used a clock pulse to time operations throughout the machine; it was a “synchronous” machine. It used some 1500 electronic valves (the Mark II had some 2400 valves).90 It had a “shift register”—a register in which the binary digits could be shifted one position to the left or right in each clock step, a common feature in later digital computers. It had bistable circuits to perform counting, binary arithmetic, and, strikingly, Boolean logical operations. This latter mirrored its most original architectural feature: a capacity to perform complicated Boolean functions. Indeed, the Colossus was designed as a “Boolean calculating machine” rather than as an “ordinary number cruncher.”91 It could also execute conditional branch operations.
Data were input through punched paper tape read by a photoelectric tape reader, whereas output was printed out on an electric typewriter.92 The only memory comprised “[e]lectronic storage registers changeable by automatically controlled sequence of operations.”93 Such automatically controlled sequence of operations—its program (although the term did not yet exist in this context)—was fed to the machine by setting switches and plugs manually.
The Colossi machines were designed as special-purpose computers, with a function to facilitate and expedite code breaking—hence, a “Boolean calculating engine.” Yet, it was sufficiently flexible “[w]ithin its own subject area” that it could be used to perform jobs that were not considered at the design stage94—although this was, apparently, a forced flexibility, for it necessitated cumbersome manual intervention.95
XIV
What was the legacy of the Colossus for the history of computing? Because of the classified nature of its mission, the work at Bletchley Park would not be known to the public for some three decades following the end of the war.96 Thus, the design details of the Colossi machines could not be transmitted to other later computer projects in Britain or abroad. In this sense, this series of machines came to an evolutionary dead end.
On the other hand, the people involved left Bletchley Park after the war, carrying with them a great deal of valuable and original knowledge, both theoretical and experiential, into their peacetime lives. Among them, at least four would be involved with computers and computing.
Newman became a professor of pure mathematics at the University of Manchester, and Good went with him.97 Manchester University (as we will see) became a hugely important site for original research in computing—and remained so into the 1950s, and through the 1960s and 1970s—and Newman had no small role in establishing this tradition. Indeed, not long after taking his position in Manchester, he applied to the Royal Society for a grant to establish a “calculating machine laboratory” in the university, which was duly awarded in July 1946. Thus was initiated the Manchester tradition. Good was involved in its early years.
Turing joined, as a “scientific officer,” the newly established mathematics division in the National Physical Laboratory (NPL) in Teddington, a London suburb.98 The mission of this division included “[i]nvestigation of the possible adaptation of automatic telephone equipment to scientific computers” and the “[d]evelopment of an electronic counting device suitable for rapid computing.”99 This appointment marked Turing’s first systematic foray into building a practical version of his “universal computing machine”—the Turing machine. He conceived and developed the detailed proposal for what came to be called the NPL’s ACE computers, with ACE being an acronym for Automatic Computing Engine.100
Michie, the classics scholar-turned-cryptanalyst, although he became a geneticist after the war, never quite forgot his interest, nurtured at Bletchley Park and shared by Turing, in chess-playing machines. In 1965, Michie was appointed professor of machine intelligence in Edinburgh University and was instrumental in making Edinburgh a leading world center in artificial intelligence.
The consequence of the Colossi projects for the future history of computer science was its people and the knowledge they held, rather than its actual machines.
NOTES
1. G. R. Stibitz. (1940). Computer. Unpublished memorandum. Later printed in B. Randell. (Ed.). (1975). The origins of digital computers (2nd ed., pp. 241–246). New York: Springer-Verlag.
2. It is no coincidence that these were the main countries battling it out during World War II—nothing like the imperative of war to facilitate machines that expedited the mathematics of warfare.
3. The literature on the evolutionary nature of creativity in technological, scientific, artistic, and literary cultures is vast—and controversial. See especially D. T. Campbell. (1960). Blind variation and selective retention in creative thought as in other knowledge processes. Psychological Reviews, 60, 380–400; P. Steadman (1979). The evolution of designs. Cambridge, UK: Cambridge University Press; G. Radnitzky & W.W. Bartley, III. (Eds.). (1987). Evolutionary epistemology. La Salle, IL: Open Court; G. Basalla. (1988). The evolution of technology. Cambridge, UK: Cambridge University Press; A. K. Sen. (1992). On the Darwinian view of progress. London Review of Books, 14; S. Dasgupta. (1996). Technology and creativity. New York: Oxford University Press; D. K. Simonton. (1999). Origins of genius: Darwinian perspectives on creativity. New York: Oxford University Press; S. Dasgupta. (2004). Is creativity a Darwinian process? Creativity Research Journal, 16, 403–413; D. K. Simonton. (2010). Creative thought as blind-variation and selective-retention: Combinational models of exceptional creativity. Physics of Life Reviews, 7, 190–194; S. Dasgupta. (2011). Contesting (Simonton’s) blind variation, selective retention theory of creativity. Creativity Research Journal, 23, 166–182.
4. Stibitz, op cit., p. 242.
5. Ibid.
6. O. Cesareo. (1946). The Relay Interpolator. Bell Laboratories Records, 23, 457–460. Reprinted in Randell (pp. 247–250), op cit., p. 247. (All citations to this and other articles reprinted in Randell will reference the reprint.)
7. Ibid.
8. Ibid., p. 239.
9. R. Moreau. (1984). The computer comes of age (p. 29). Cambridge, MA: MIT Press.
10. J. Juley. (1947). The Ballistic Computer. Bell Laboratories Records, 24, 5–9. Reprinted in Randell (pp. 251–255), op cit., p. 251.
11. Cesareo, op cit., p. 249.
12. Juley, op cit., p. 253.
13. Cesareo, op cit., p. 249.
14. Juley, op cit., p. 254.
15. Cesareo, op cit., p. 250.
16. Juley, op cit., p. 254.
17. Randell, op cit., p. 239.
18. Ibid.
19. F. L. Alt. (1948a). A Bell Telephone Laboratories computing machine: 1. Mathematical Tables for Automatic Computation, 3, 1–13. Reprinted in Randell (pp. 257–270), op cit., p. 257.
20. For more on technological complexity see G. Basalla, op cit. S. Dasgupta. (1997). Technology and complexity. Philosophica, 59, 113–139.
21. Alt, op cit., p. 257.
22. F. L. Alt. (1948b). A Bell Telephone Laboratories computing machine: II. Mathematical Tables for Automatic Computation, 3, 69–84. Reprinted in Randell (pp. 271–286), op cit., pp. 283–284.
23. Alt, 1948b, op cit., p. 277.
24. Ibid.
25. Ibid., p. 276.
26. Ibid.
27. Alt, 1948a, op cit., p. 270.
28. C. S. Boyer. (1991). A history of mathematics (2nd ed., Rev., p. 579). New York: Wiley.
29. C. E. Shannon. (1940). A symbolic analysis of relay and switching circuits. Unpublished thesis, Department of Electrical Engineering, MIT, Cambridge, MA. For some reason, although Shannon submitted the thesis in 1937, it was approved formally in 1940.
30. Stibi
tz, op cit., pp. 243–244.
31. R. K. Richards. (1955). Arithmetic operations in digital computers (p. 33). Princeton, NJ: Princeton University Press.
32. Ibid.
33. Ibid.
34. L. J. Comrie. (1928). On the construction of tables by interpolation. Monthly Notices of the Royal Astronomical Society, 88, 506–523. L. J. Comrie. (1932). The application of the Hollerith tabulating machine to Brown’s tables of the moon. Monthly Notices of the Royal Astronomical Society, 92, 694–707.
35. H. H. Goldstine. (1972). The computer from Pascal to von Neumann (p. 109). Princeton, NJ: Princeton University Press.
36. Ibid.
37. H.. H. Aiken. (1975). Proposed automatic calculating machine. Reprinted in Randell (pp. 191–197), op cit. (original work published 1937). Page citation to this chapter refers to the Randell reprint.
38. Ibid., p. 192.
39. Ibid.
40. Ibid., pp. 192–193. Aiken also listed a fourth, more technical, mathematical requirement that we can ignore here.
41. Ibid., p. 193.
42. Randell, op cit., p. 187; Goldstine, op cit., p. 111.
43. H. H. Aiken & G. M. Hopper. (1975). The Automatic Sequence Controlled Calculator [in three parts]. Electrical Engineering, 65, 384–391, 449–454, 522–528 (original work published 1946). Reprinted in Randell (pp. 199–218), op cit., See footnote, p. 199. All page citations to these articles refer to the Randell reprint.
44. Ibid.
45. Ibid., p. 201 ff.
46. The number of significant digits indicate the range and precision of the real numbers that can be represented. For example, the value of π as a real number, 3.14285 …, can be represented to more decimal digits with an increase in the number of significant digits.
47. Aiken & Hopper, op cit., p. 201.
48. Moreau, op cit., p. 30.
49. Aiken, op cit.